Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. In FIGS. 1 and 2, a magnetic disk data storage system 10 includes a sealed enclosure 12, a disk drive motor 14, and a magnetic disk, or media, 16 supported for rotation by a drive spindle 17 of motor 14. Also included are an actuator 18 and an arm 20 attached to an actuator spindle 21 of actuator 18. A suspension 22 is coupled at one end to the arm 20 and at another end to a read/write head 24. The suspension 22 and the read/write head 24 are commonly collectively referred to as a head gimbal assembly (HGA). The read/write head 24 typically includes an inductive write element and a magneto-resistive read element that are held in a very close proximity to the magnetic disk 16. As the motor 14 rotates the magnetic disk 16, as indicated by the arrow R, an air bearing is formed under the read/write head 24 causing the read/write head to lift slightly off of the surface of the magnetic disk 16, or, as it is commonly termed in the art, to “fly” above the magnetic disk 16. Data bits can be written or read along a magnetic “track” of the magnetic disk 16 as the magnetic disk 16 rotates past the read/write head 24. The actuator 18 moves the read/write head 24 from one magnetic track to another by pivoting the arm 20 and the suspension 22 in an arc indicated by arrows P. The design of magnetic disk data storage system 10 is well known to those skilled in the art.
FIG. 3 shows a cross-sectional view of a read/write head 24. The read/write head 24 includes a write element 30 for writing data bits to the magnetic disk and a read element 32 for reading the data bits. The write element 30 includes a yoke 34 and one or more layers of electrically conductive coils 36 wound around the yoke 34. In operation, an electric current is passed through the coils 36 to induce a magnetic field in the yoke 34. The yoke 34 includes a lower pole 38 connected to an upper pole 40 by a back gap 42 at a back gap end. The lower and upper poles 38, 40 oppose each other across a write gap 44 at an air bearing end. The yoke 34 is commonly formed of ferromagnetic materials.
The read element 32 includes a first shield 46, a second shield 48, a read insulation layer 50 disposed between the first shield 46 and the second shield 48, and a read sensor 52 disposed within the read insulation layer 50 and exposed at an air bearing surface (ABS). In some designs, often referred to as “merged head” designs, second shield 48 and lower pole 38 are the same layer. In other designs, such as the one shown in FIG. 3, a thin insulating layer 54 separates the second shield 48 from the lower pole 38.
In existing read sensors (e.g., current perpendicular to plane or “CPP” giant magneto-resistance or “GMR” film stack read sensors) with conventional magnetic material such as CoFe and CoFeB, the read signal is small with limited CPP GMR ratio (less than 2% as usual) that does not meet requirements for large signal to noise ratio (SNR) applications. For those with Heusler alloy material based read sensor elements, a large CPP GMR ratio up to tens of percentage is available but with bulky stack design and epitaxial growth of films on crystalline oriented MgO (100) substrates. These read sensors are not suitable for hard drive and magneto-resistive random access memory (MRAM) applications in terms of requirements on small shield to shield spacing and improved performance of devices using such read sensors for high areal density recording.
Conventional efforts utilizing Heusler alloy materials in CPP GMR devices have explored widely the potential and possibility for enhanced output signal and largely improved SNR. However, the output signal from such devices remains on the low side, in particular for small shield to shield spacing form factors. The major challenges lie on the fact that crystal structure of Heusler alloy multi-layers need to be modulated such that they are compatible with L21/B2 ordering to realize half metallicity and large spin polarization with epitaxial growth of thin films. Accordingly, what is needed is an improved magnetic storage element that provides improved electrical performance while providing small shield to shield spacing on a NiFe substrate.